Saturday, 17 October 2015

Kenyan camel coronaviruses...

Two studies have now found antibodies from Middle East respiratory syndrome coronavirus (MERS-CoV)-like coronaviruses in dromedary camels (DCs). The "like" bit reflects that unless we have some sequence, we can't say for certain that the virus that infected those camels in the past, causing them to respond with these antibodies, was a MERS-CoV variant. The virus(es) may have been a different camel CoV that just so happens to share some antigens and is detected by MERS-CoV-"specific" antibody detection tests. The old story of "we don't know what we don't know" can perhaps be extended here to "we can't validate a test against viruses we haven't found yet". Or that may just be too nerdy.

Anyhoo, we have two papers to look at here. 

Antibodies against MERS coronavirus in dromedary camels, Kenya, 1992-2013

This paper went into the August edition of Emerging Infectious Diseases, authored by Corman and team (online much earlier but no way to track that thanks to no date of ePub ahead of print - loud sigh!) from Germany, Kenya, the Netherlands and Sweden.[1]

The introduction sets the scene for a paper seeking to know about where the MERS-CoV we know and love today, may have come from to be so common amongst camels. We suspect that this could be from another animal in its current form, or by recombination and mutation from a different ancestral form that has yet to be discovered in an animal (or human). This study seeks out MERS-CoV or a MERS-CoV like virus, or an ancestor, from camels in Kenya using their blood to look for footprints of previous infection - in this case, antibodies.

774 DC blood and stored sera collected from three regions of Kenya between 1992 and 2013 were subjected to a multi-step testing process:
  1. All samples, diluted 1:100, were screened using MERS-CoV spike protein subunit 1–based ELISA (rELISA; described before at [2])
    .228 of 774 (29%) were positive
  2. The 228, diluted 1:40, were next examined using a recombinant immunofluorescence assay using Vero cells expressing MERS-CoV spike protein (rIFA; described before at [3]
    .213 of 228 (93%; 28% of the 774) were still positive in the second tier of testing
  3. The third tier of testing of samples diluted between 1:80 and 1:800 used a highly specific MERS-CoV microneutralization assay (MNT assay; also previously described in [3])
    .119 of 213 (56%; 15% of the 774) had titres (dilutable levels) greater than or equal to 1:80 and 14 had titres above 800
    .Some counties of Kenya had 60-100% of samples test positive 
Figure 1. From Corman et al, Emerg Infect
Dis. 2014 Vol 20, No 8. 1319:1322.[1]
Click on image to enlarge.
North-eastern and northern regions generally had higher titres (Fig.1).These are regions closer to other countries with known antibody-positive camels (Egypt, Sudan, Somalia and Ethiopia). Further, nomadic camels from the East had higher antibody titres than those farmed in the north-west of the Rift Valley. Nomadic camels are taken across borders for trade.[2] DCs that had been kept isolated since 1998 were negative signs of past MERS-CoV virus. 

Adults had higher antibody levels than juveniles - presumably because infections happen when the DCs are young, producing the antibodies we detect in adult DCs.

Figure 2. Quote from [1]
Click on image to enlarge.
Camel density was also important. More camels were antibody positive in areas with higher densities of camels - also presumably because virus can spread better from one infected DC to others when more DC contacts are around. Similar story for humans, a contributing factor for those super-spreading conditions. The authors also made a comment that is very important to the answer the question of why human cases have not been found in areas with animal infections (see Figure 2).

Moving on to the next publication from Kenya.

Serological Evidence of MERS-CoV Antibodies in Dromedary Camels (Camelus dromedaries) in Laikipia County, Kenya

This one just came out on PLOS|ONE authored by Deem and colleagues from the United Stets of America, Kenya, New Zealand and the Netherlands.[4]

The introduction also reminds us that understanding MERS-CoV in camels in countries with herds, can help us assess and manage the risk for humans in those countries. In this case, Kenya has over 3 million DCs and mean and milk is worth $USD 11 million a year. These figures that may help you understand why DC interests don't want to have a significant human pathogen harboured by their animals.

This study is based in Laikipia County, almost in the centre of Kenya (Fig 1), which has a growing camel population. 

335 camels were sample from 9 easily accessed herds.

  1. All samples, diluted 1:20, were screened using a MERS-CoV, severe acute respiratory syndrome (SARS)-CoV, human CoV (HCoV)-OC43 spike domain S1 antigen protein-microarray method used previously by this group [5,6,7,8,9]
    _46.9% of DCs were seropositive (had antibodies) including at least 1 animal per herd
    _60.8% of adult DCs were seropositive and 21.3% of the juvenile animals
    _bovine CoV (tested for by including the HCoV-OC43 antigens) seroprevalence was high, as it often is in DCs
    _this study did not see a significant difference in seroprevalence between nomadic herds or those managed in more commercial ways and no differences between different degrees of herd isolation
Figure 3. Quote from [4]
Click on image to enlarge.
The authors concluded that these herds were being exposed to MERS-CoV (or a similar virus) on an ongoing basis, even though they were not near borders and at lower densities that the more northern sites reported by the Corman et al. study above. They did not feel these disparities were due to diagnostic differences and that the DC densities in Lakipia County were sufficient to maintain virus circulation. 

The conclusion noted the need to get sequence from this virus or these viruses n order to see whether they are the MERS-CoV we know, a different clade of MERS-CoV variants or another virus entirely. That sort of information can't be gleaned from antibody studies and so RT-PCR methods are needed.

The report wrapped up with a comment about a lack of reporting of human cases (Fig.3).

Clearly, camels are commonly infected by MERS-CoV or a close relative in parts of Africa and the Arabian Peninsula which receives camel imports from Africa. 

Also very clearly, DCs survive the experience apparently fine and unharmed lending more support for MERS-CoV in DCs being just a "camel cold". The camels do not need to be culled the way we do to other ill virus-infected animals (I'm looking at you chooks with high pathogenicity influenza A(H5N1) virus..or other flu viruses). We just need to remove camels from humans - or better manage the interactions we have to have. It's not rocket science but it will take thoughtful, considered and collaborative discussions.

  1. Antibodies against MERS coronavirus in dromedary camels, Kenya, 1992-2013
    Corman VM, Jores J, Meyer B, Younan M, Liljander A, Said MY, Gluecks I, Lattwein E, Bosch BJ, Drexler JF, Bornstein S, Drosten C, Müller MA.
  4. Serological Evidence of MERS-CoV Antibodies in Dromedary Camels (Camelus dromedaries) in Laikipia County, Kenya
    Sharon L. Deem , Eric M. Fèvre, Margaret Kinnaird, A. Springer Browne, Dishon Muloi, Gert-Jan Godeke, Marion Koopmans, Chantal B. Reusken